Open hearth furnace control



Mme 8, 1932. J. K. MAWHA 193487384 OPEN HEARTH FURNACE CONTROL FiledSept. 26, 1930 3 Sheets-Sheet l MAW/1 ATTORNEYS March 8, 1932. J K.MAWHA 1,848,184

OPEN HEARTH FURNACE CONTROL Filed Sept. 26, 1930 3 Sheets-Sheet 2 March8, 1932. J. K. MAWHA OPEN HEARTH FURNACE CONTROL Filed Sept. 26, 1930 3Sheets-Sheet Patented Mar. 8, 1931? UNITED STATES PATENT OFFICE JAMES K.MAWHA, OF MAPLEWOOD, NEW JERSEY, ASSIGNOR TO SHOOT ENGINEERINGCORFOIRATION OF NEW YORK, N. Y., A CORPORATION OF DELAWARE OPEN HEABTHFURNACE CONTROL Application filed September 26, 1980. Serial No.484,489.

My invention relates to the control of the air supply in open hearthfurnaces, and comprises regulating apparatus particularly adapted toautomatically control the air supplied to open hearth furnaces of thereversible type. My invention preferably includes a master control meansfor permitting adjustment from a central point of the total fuel and airsupplied to the furnace as well as the ratio of fuel to air, and isequally applicable to furnaces burning liquid fuel, or gas, or acombination of both.

In certain types of regenerative furnaces, two stacks are provided, eachincluding a section made in the form of a Venturi pipe and provided witha controlling damper in the neck of the Venturi section. In thesefurnaces air is delivered to the furnace at apoint below the Venturisections. Closure of the damper in one stack causes the air to bedeflected into the furnace as a forced draft, simultaneously, the damperin the opposite stack being open, the air passes through the Venturisection, serving as induced draft to withdraw the gases from thefurnace. These dampers are so connected that when one is open the otheris closed, thus interchanging the function .of the air supply to each.Correlation of the air supplied to each stack in this type of furnace isan essential element in the efficient operation of the furnace, it beingnecessar at all times to insure a supply of air to the urnace properlyproportioned to the fuelsupply, and an exhaust of gases from the furnacesuch that the proper pres sure conditions will 'exist within the furnacechamber.

It is a practice with this type of furnace to associate a blower witheach stack, the

blower alternately serving the purpose of a Y forced draft for aninduced draft fan. Heretofore the operation of the blowers .under theseconditions has required such a wide speed range to obtain the pro ervolume range that it has been costly and inefficient to accuratelyproportion the air or make the regulators respond to slight pressurefluctuations within the furnace.

My invention particularly relates to means for controlling the airsupply so that a wide 5 volume range will be obtained, permitting theversing damper therein in combination with air regulators and soarranged that regardless of the location of the blowing apparatus thereversing damper intersects the conduits at a point between the furnaceand the points at which the air is regulated, so dividing the conduitthat it alternately connects the regulated air supplies with theopposite stacks. For a better understanding of my invention referencemay be had to the accompanying drawings of which:

Figure 1 diagrammatically illustrates an embodiment of my inventionapplied to a liquid fuel burning furnace in which two constant speedblowers are used, the air supply to the furnace being. controlled byregulating the inlet air to the blowers;

Fig. 2 diagrammatically illustrates an embodiment of my inventionapplied to a liquid fuel burning furnace in which two constant speedblowers are used, the air supply to the furnace being controlled byregulating the discharge from the blowers;

Fig. 3 is a variation'of some of the ap aratus of Fig. 2 in whichvariable speed Instead of constant speed blowers are em-.

ployed;

Fig. 4 is a variation of some of the apparatus of Fig. 2 in which apositive displacement blower is employed to supply the forced draft airsupply; and

Fig. 5 diagrammatically illustrates one embodiment of my inventionapplied to a liquid fuel burning furnace in which one constant speedblower discharges into a common conduit, the air su ply to the furnacebeing controlled by regu ating the discharge from the fan.

The master and the fuel control regulators shown in Fig. 1, being thesame for each embodiment, have been omitted from Figures 2 and 3 forsimplicity. The regulators are'diagrammatically illustrated, forsimplicity, as comprising a balancing lever ar ranged for direct controlof the associated damper or valve in response to forces warying as afunction of the element controlled and in response to a forcetransmitted to the lever by the master controller. Preferably theseregulators would be of the anti-hunting balancedtype employing auxiliarypower fluid for operating the controlled elements. As such regulatorsare now well known in the art it is not believed necessary to illustrate or describe the same in detail. For example, these regulators maytake the form illustrated in Fig. 2 of Smoot Reissue Patent N 0. 16,507,dated December 21, 1926.

Likewise the particular construction of the master controller isimmaterial, but preferably I employ a construction similar to thatdisclosed in the aforementioned reissue patent. As shown in Fig.1, themaster controller 60 may comprise a chamber 60a into which air underpressure is supplied through a throttled pipe 606 from any suitablecompressor or the like (not shown). A cup valve 600 permits leakage ofair from the chamber in an amount dependent upon the pressure actingthereon and upon the tension of a spring 61 tending to raise valve 600against a downward pressure of the air in chamber 60a. Spring 61 has oneend attached to a pivoted lever 62 to which valve 600 likewise attachedand has its other end attached to a rack 63. The position of rack 63 andhence the tension of spring 61, is adjusted manually by means of a handwheel64 mounted on a pinion meshing with the teeth of rack 63. Aplurality of chambers 66 receive air under pressure from chamber 60athrough restricted orifices 68. Air from chambers 66 bleeds toatmosphere through controlled orifice valves 67 a, 67 b, 670.

The open hearth furnace 1 is diagrammatically illustrated in Fig. 1, ashaving a furnace chamber 2 and regenerative checker brick passages 3 and3 leading to stacks 4 and 4' respectively. Stacks 4 and 4; are eachfitted witha Venturi section 5 and 5' and damper 6 and 6' fitted totightly close or completely open the passage through the Venturisection. A blower 7 supplies air through conduit 8 terminating in thestack under damper 6. \Vhen 6 is closed the air is deflected and acts asa forced draft thror the furnace. Simultaneously air is being suppliedby blower 7' through conduit 8.

The damper 6 is open and the air jet serves as an exhauster drawing thegases from the furnace 2. The dampers 6 and .6 are suitablyinterconnected so that upon reversing the furnace cycle the dampersreverse and the air supplied performs the opposite. functlon.

The accurate control of the through conduits 8 and 8 is essential forellicient operation. Referring to Figure 1, I obtain this result byproviding two constant speed blowers 7 and 7 their intakes 9 and 9leading to an intersection where, due to the position of damper 12, theyinterconnect with the intake conduits 10 and 11 respectively, 910serving as an inlet conduit for the forced draft and 9'11 serving as aninlet for the induced draft. By reversing damper 12 to the dottedposition conduit 10 would be connected to 9 and conduit 11 connected to9. In this manner the forced draft air supply is always drawn throughconduit 10 and the induced draft air supply is always drawn throughconduit 11 regardless of the cycle of the furnace and the regulators 15and 18 maintaining the same function throughout. A damper 14 islocatedin 10 and controlled by regulator 15, which acts to adjust thedamper and keeps a fixed relation between the master pressuretransmitted through pipe 19 to chamber 15a and the differential airpressure across a construction 16 transmitted to chambers 15?) and 150through pipes 20 and 21. A damper 17 is located in 11 and controlled byregulator 18 which acts to adjust the damper and maintain a fixedrelation between the furnace pressure transmitted through pipe 22 tochamber 181; and atmospheric pressure.

In the position illustrated in Figure 1, blower 7 is supplying theforced draft. drawing air from atmosphere through conduit 9-10 anddischarging it into conduit 8. The stack damper 6 being closed, the airis deflected and passes through the checkerbrick 3 into the furnace 2.Simultaneously blower 7 is supplying induced draft, drawing air fromatmosphere through conduit 9'11 and discharging it into conduit 8. Thestack air supplied damper 6" being open, the air jct passes through theVenturi section drawing the gases of combustion with it.

As diagrammatically illustrated, an increase in air flow will cause anincrease of pressure in chamber 157) causing arm 30 to move in adirection to close damper 14, restricting the orifice and reducing theflow to normal. If the master calls for an increase in air flow, thepressure increase in chamber 15a will cause arm 30 to move in adirection to open damper 14, increasing the orifice and permitting anincrease of flow. An increase of pressure in furnace 2 will increase thepressure in chamber 18a causing arm 31 to move in a direction which willopen damper 17, permitting an increase of air supply, increasing t-heair flow through the Venturi section withdrawing the gases of combustionand bringing the furnace pressure to normal. The volume supplies of airto the blowers may thus be varied from substantially nil when dampers 14and 17 are closed to the total volume obtained when the dampers are.

wide open.

Figure 1 illustrates the air control acting in conjunction with the fuelcontrol. The fuel is supplied to burner 32 from the branch line 33 whichreceives its supply from the main fuel line 34. The fuel is injected bysteam delivered from a main supply 36, through branches 37 to burner 32.Regulator 40 controls valve 41 adjusting the fuel supply to maintain afixed relation between the pressure transmitted through pipe 34, fromthe master controller and the difl'erential across a constriction 42, inpipe 34, transmitted to regulator 40 through pipes 43-and 44. Theinjector steam valve 45 is varied by regulator 46 to maintain a fixedrelation between the pressure from the master controller pressuretransmitted through pipe 47 and the steam pressure transmitted throughpipe 48.

When the cycle of the furnace is reversed it is necessary to reversedamper 12 in con duit 9--9. This may be done by any manual or mechanicalmeans, but preferably it is arranged to work in conjunction withcylinders 51 and 51 which reverse stack dampers G and 6'. Asillustrated, an auxiliary liquid or air transmits pressure from a source(not shown) through pipe 53 to the relay valve 54 which in the positionshown permits the pressure to be transmitted to the cylinders throughpipe 55, pipe 56 being open to a drain 57. Reversing lever 54a willconnect pipe 53 with pipe 56 and 55 with drain 57, pressure will then betransmitted to' the opposite ends of the cylinders, opening stack damper6, closing stack damper 6', and swinging damper 12 to the dottedposition. Blower 7' will now draw air through 9'1Q and serve as a forcedraft blower, whereas 7 will draw air through 9--11 and act as ancxhauster. The fuel supply may be changed manually by reversing valves4950 and 49'-'50', or they may likewise be controlled by valve 54 or byany other suitable mechanical means.

In the embodiment shown in Figure 2. two constant speed blowers areagain employed but it difiers from Figure 1 in that the function of theblowersas well as the regulators remain constant. and damper 12 dividesthe conduitson the discharge side of the blowers. whereas in Figure 1 itdivides the conduit on the inlet side. As illustrated. blower 1discharges into conduit 3-8, stack damper 6 being closed and the airpasses into the furnace as forced, draft. Simultaneously blower 2discharges into conduit 4- stack damper 6' being open the air passesthrough the Venturi section and produces an induced draft. A damper 14inserted in conduit 3 is controlled by regulator 15 through arm 30.Regulator 15 acts to maintain a fixed relation between the masterpressure transmitted to 15a through pipe 19 and a differential airpressure across constriction 16 transmitted to chambers 15b and 150through pipes 20. 21. Damper 17 inserted in discharge conduit 4 iscontrolled by regulator 18 which acts to maintain a fixed relationbetween the furnace pressure transmitted to chamber 180 through pipe 22and atmospheric pressure. An increase in air flow across constriction 16will cause regulator 15 to move arm 30 in adirection which will closedamper 14 restricting the conduit and reducing the air flow to normal.,An increase of pressure from the master will cause arm 30 to move in adirection to open damper 14 permitting a greater flow of air to thefurnace. An increase in furnace pressure will be transmitted throughpipe 22 to chamber 18a causing it to move arm 31 in a direction to opendamper 17 increasing the induced draft and withdrawing the gases fromfurnace chamber 2 until the pressure equalizes.

Cylinder 13 which operates damper 12 may be controlled by manual ormechanical means but preferably is operated in conjunction withcylinders 51-51' operating dampers 6-6, as explained and illustrated inFig. 1. If damper 12 is reversed to the dotted position, stack damper 6opened and 6 closed, the operation of the furnace is reversed but thefunction of the two blowers remain constant. Blower 1 will continue thesupply of forced draft through conduit 3 but damper 12 now deflects theair into the conduit 8' and blower 2 will continue the supply of induceddraft through conduit 4, but damper 12 now deflects the air into conduit8, the functions of regulators 15 and 18 also remaining constant.

Fig. 3 is a variation of Fig. 2 and as illustrated regulator 15 acts toadjust the rheostatof a variable speed motor which drives blower 1.- Asthe blower always supplies forced draft, the speed range may be reducedto a minimum by proper selection of'the motor. The fan for induced draftmay be similarly controlled.

Fig. 4 illustrates another variation of Fig. 2 in which the forced draftis supplied by a positive displacement blower. The regulator 15 now actsto maintain a fixed relation between the master pressure and the speedof the blower. adjusting arm 30 to regulate a rheostat controlling thespeed of the blower. the induced draft air supply may be con trolled asshown in Fi 2. or the blowermay be driven by a variable speed motor witha regulator controlled field rbeostat.

Fig. 5 is another embodiment of my invention differing from the othersin that only one constant speed blower is used dischargiug into a commonconduit :2 which divides into legs 2a and 2b which alternatelyconnectwith conduits 8 and 8 dependent upon the position of reversingdamper 12. As illustrated in Fig. 5, 2a connects with conduit 8, stackdamper 6 being closed the air acts as a forced draft, and 2?) beingconnected to 8 and stack damper 6' being open the air supplied acts asan induced draft. A reversal of damper 12 in conjunction with stackdampers 6 and 6' as previously explained will connect 2a with 8 and 2bwith 8, but it will be noted that the forced draft is always suppliedthrough leg 2a and the induced draft through leg 25. Itegulators 1:")and 18 per-v form the same functions as explained in Flg. 2.

I have now described several embodiments of my invention. It will benoted that in all embodiments the functions of the regulators are notinterchanged, the ducts being so arranged that air for forced draft isalways drawn or discharged through the same conduit, likewise air forinduced draft is always drawn or discharged through the same conduit, asfar as the reversing damper which intersects the conduits andalternately deflects the air to opposite ends of the furnace. Thispermits the cross-section areas of the conduits which always supplyeither p y forced or induced draft to be properly proportioned to meetthe required conditions, thus minimizing the speed range of the blowersand the range of action required of the regulators. It furthereliminates the necessity of individual fans for each furnace except incases where it is desirable to control the draft by controlling thespeed of the blowers- Where the draft is controlled by regulated dampersin the forced draft and induced draft sections of the individual furnaceair supply system, the air could be drawn from a common source of supplyfor several furnaces. thus reducing the number of blowers required.

As shown in the embodiment of Fig. l, and equally applicable to theother embodiments, the air control may be combined with a mastercontroller whereby the air control may be maintained at any-desirableratio in proportion to the fuel supply, whether liquid or gas. or acombination of the two.

I claim:

1. In a reversing furnace of the type wherein a pair of conduits areadapted to be alternately utilized to deliver air under pres sure forforced draft or air for inducing withdrawal of the gases from thefurnace, the combination comprising means for creating the drafts, aforced draft air supply duet, an inducing draft air supply duct,separate means for regulating the drafts in said ducts,

and means for connecting the forced draft duct with either one of saidconduits and simultaneously connecting the inducing draft duct with theother of said conduits.

2. The combination according to claim 1 including a regulator for thefuel supply to the furnace chamber adapted to maintain a predeterminedrate of flow of fuel thereto and a: master controller connected to saidfuel regulator and to the means associated with the said draftregulators for adjusting the total fuel and the air supplies to thefurnace and the ratio therehetween.

3. The combination according to claim 1 wherein the furnace is providedwith a pair of burners and with liquid fuel and injection steam supplypipe lines therefor branching to each of said burners, and wherein thecontrol system includes a regulator adapted to maintain the flow ofliquid fuel through the supply pipe in predetermined ratio with the airflow to the furnace and a regulator for the steam supply pipe adapted tomaintain the pressure of the injection steam in proportion to the flowof fuel.

i. In a reversing furnace of the type wherein a pair of conduits areadapted to be alternately utilized to deliver air under pressure forforced draft or air for inducing withdrawal of the gases from thefurnace, the combination comprising means for creating the draftswhereby there is one source of supl of air under pressure for both theforced draft and the inducing draft, a forced draft air supply duct, aninducing draft air supply duct, separate means for regulating the draftsin said ducts and means for connecting the forced draft duct with eachof said conduits and simultaneously connecting the inducing draft ductwith the other of said conduits.

5. In a reversing furnace of the type wherein a pair of conduits areadapted to be alternately utilized to deliver air under pressure forforced draft or air for inducing withdrawal of the gases from thefurnace, the combination comprising means for creating the draftswhereby there is one source of supply of air under pressure for forceddraft and another source of supply of air under pressure for induceddraft, a forced draft air supply duct, an inducing draft air supplyduct, separate regulators for controlling the drafts in said ducts, andassociated therewith means for applying to the regulator controlling theforced draft a differential pressure varying with the'rat-e of adifferential pressure varying with the pressure in the furnace. andmeans for connecting the forced draft duct with each of said 6. In areversing furnace of the type wherein a pair of conduits are adapted tobe alternately utilized to deliver air under pressure for forced draftor air for inducing withdrawal of the gases from the furnace, thecombination comprising a forced draft air supply duct, an inducing draftair supply duct, means for creating the drafts whereby there is oneblower for supplying the forced draft and another blower for supplyingthe induced draft, a regulator for each blower, and associated therewithmeans for applying to the regulator controlling the blower supplying theforced draft a differential pressure varying with the rate of air flowto the furnace, and to the regulator controlling the blower supplyinginduced draft a differential pressure varying with the pressure in thefurnace, and means for connecting the forced draft duct with each ofsaid conduits, and simultaneously connecting the inducing draft ductwith the other of said conduits.

' 7. In a reversing furnace of the type wherein a pair of conduits areadapted to be alternately utilized to deliver air under pres sure forforced draft or air for inducing withdrawal of the gases from thefurnace, the combination comprising means for creating ber to which fuelis supplied and from which the air from the other blower induces with-JAMES K.

the drafts whereby one blower supplies air under pressure for bothdrafts to one conduit, and another blower supplies air under pressurefor both drafts to the other conduit, a forced draft air supply duct,,an inducing draft air supply duct, means for regulating the drafts insaid ducts, and means for connecting the forced draft duct-with each ofsaid conduits and simultaneously connecting the inducing draft ductwith' the other of said conduits. i

. 8. In areversing furnace of the type wherein a pair of conduits areadapted to be alternately utilized todeliver air under pressure forforced draft or ai'r'for inducing the withdrawal of gases from thefurnace, the combination of a blower connected to discharge air underpressure into one of said conduits, a second blower connected todischarge air under pressure to the other conduit, a forced draft airsupply intake duct, an inducing draft air supply intake duct, separatemeans for regulating the drafts in said ducts and means for connectingthe forced draft intake duct with the intake of either of said blowersand simultaneously connecting the inducing draft intake duct with theintake of the other of said blowers. 9. In combination with a reversingfurnace of the type wherein a pair of continuously operating blowerssupply air under pressure into damper controlled Venturi sections of apair of stacks and the furnace is reversed by reversing the position ofthe dampers in the stacks to cause the 'air delivered by one blower tobe deflected at the closed damper and to thereupon pass into the meltingcham-

